It is currently known and quite common to preload tapered roller bearings/antifriction bearings that rotatably support a pinion shaft in a differential gear assembly. Such differential gear assemblies are typically used in vehicles for delivering torque to the driven wheels. The engine typically delivers its torque through a transmission to a drive shaft which is coupled to the pinion shaft in the differential housing. The pinion shaft then delivers the torque in a known and customary manner to the drive axle connected to the driven wheels.
The pinion shaft is mounted and supported in the differential housing with a pair of tapered antifriction roller bearings. It is desirable to preload the tapered antifriction roller bearings to eliminate play or axial and radial free motion between the shaft, bearings and housing. The bearing preload is determined by measuring the torque required to rotate the pinion shaft and bearings within the housing. This bearing preload must be enough to prevent the bearings from gaining play and must not be so great so as to cause the bearings to overheat. Thus, a proper preload condition is required for maximizing the life of the pinion shaft and differential gear assembly. Depending on the size of the differential gear assembly, type of bearing assembly, materials, etc., the manufacturer determines the ideal preload value for maximizing the life of the differential gear assembly.
Various apparatus and methods have been devised and are in use for preloading tapered antifriction roller bearings. One such method is described in Witte, U.S. Pat. No. 5,125,156 wherein, after a pinion shaft and bearings are assembled in the housing, the assembly is placed in an upright condition with the pinion shaft gear facing downwardly and the pinion threaded end, nut and yoke extending vertically upwardly. In this position, the pinion gear rests on a rotatable support and a torque sensor restrains rotational motion of the assembly housing. The yoke is coupled to a drive head and is rotatably driven along with the pinion shaft in a clockwise direction. The nut is engaged with a socket which is also rotated clockwise at a slightly greater angular velocity thereby tightening the nut onto the pinion shaft and causing a spacer on the pinion shaft between the bearings to collapse and the bearings to be preloaded. Thereafter, by simultaneously rotatably driving both the yoke and pinion shaft along with the nut at the same clockwise angular velocity, a sensor which is located so as to restrain rotational motion of the housing provides an output reading which is proportional to the pinion preload condition.
Another method for preloading tapered antifriction roller bearings is described in Bonvollet U.S. Pat. No. 5,579,570 wherein, again, after a pinion shaft and bearings are assembled, the housing assembly is placed in an upright condition with the pinion shaft threaded end, nut and yoke extending vertically upwardly. Here however, the pinion shaft gear is not rotatably supported. A low torque drive assembly is coupled to the yoke so as to rotatably drive the yoke and pinion shaft in a clockwise direction. A high torque drive assembly is supported on the low torque drive assembly and engages and rotates the nut in a clockwise direction at a slightly greater clockwise angular velocity thereby tightening the nut onto the pinion shaft and causing the spacer on the pinion shaft between the bearings to collapse and the bearings to be preloaded. The high torque drive assembly is supported on the low torque drive assembly and is prohibited from independent movement relative to the low torque drive assembly. A sensor restrains the low torque drive assembly from rotation relative to the housing. By simultaneously rotating both the low torque drive assembly and the high torque drive assembly at the same speed in a clockwise direction, after the nut and bearings have been tightened, the sensor output is representative of the bearings preload condition.
As can be appreciated, although these prior apparatus and methods suffice in driving the pinion nut, tightening the bearings and measuring the preload condition of the bearings, they have shortcomings and drawbacks. Substantial effort in controlling the nut driving assembly at a slightly greater angular velocity than the yoke driving assembly is required. Further, during pinion preload measuring, the yoke and drive nut assemblies must rotate substantially precisely at the same angular velocity in the clockwise direction or risk potential inadvertent tightening and unwanted increase preload of the bearings. Accordingly, a need exists for an apparatus and method for preloading an antifriction bearings set which can relatively easily and inexpensively be controlled for driving the nut onto the pinion shaft and tightening the antifriction bearings to a preload condition and which operates efficiently and reliably in achieving the desired preload condition.